1. Field of the Invention
The present invention relates generally to high speed data transmission systems. More particularly, embodiments of the present invention relate to systems and methods that serve to maintain the integrity of one or more data signals by checking and adjusting the polarity of the data signals as required to compensate for undesirable data signal effects that may result from various internal or external conditions.
2. Related Technology
Many high speed data transmission networks rely on optical transceivers and similar devices for facilitating transmission and reception of digital data embodied in the form of optical signals. Typically, data transmission in such networks is implemented by way of an optical transmitter, such as a laser, while data reception is generally implemented by way of an optical receiver, an example of which is a photodiode.
Various other components are also employed by the optical transceiver to aid in the control of the optical transmit and receive components, as well as the processing of various data and other signals. For example, such optical transceivers typically include a driver configured to control the operation of the optical transmitter in response to various control inputs. The optical transceiver also generally includes a post-amplifier configured to perform various operations with respect to certain parameters of a data signal received by the optical receiver.
In conventional optical transceivers, the driver and post-amplifier are implemented by way of separate integrated circuits (“IC”) that are placed on a printed circuit board (“PCB”) and electrically connected with each other and with the optical transmitter and receiver. One drawback to such an approach however, is that the two separate ICs take up a relatively large amount of space on the PCB, often necessitating the use of a two-sided PCB. This type of approach is problematic however, at least because such two-sided PCBs are generally more expensive and more difficult to manufacture than a single-sided PCB.
Another concern with conventional optical transceivers relates to the control circuit interface typically employed. Generally, the control circuit serves to direct both the processing of various data signals, as well as certain operational aspects of the optical transmitter and receiver. In conventional optical transceivers, the driver and post-amplifier communicate with the control circuit by way of corresponding analog interfaces. One problem with such an arrangement is that the need for multiple interfaces necessarily requires additional PCB space and complicates the manufacturing process.
As suggested by the foregoing, the implementation of post-amplifier and driver functionality in the form of discrete components gives rise to some redundancy in terms of the various components that are required. In addition to necessitating, for example, multiple interfaces, such arrangements also typically require respective sets of registers and monitoring circuits for the post-amplifier and for the laser driver. As in the case of the interfaces, these additional components take up additional space on the PCB and increase manufacturing costs and complexity.
With more particular reference to the analog interfaces between the control circuit and the post-amplifier and laser driver, it was suggested earlier that implementation of such analog interfaces requires the control circuit to communicate with the optical transceivers by way of analog signals. However, the use of such analog signals, at least where such use is required by the employment of analog interfaces, may limit the functionality of the control circuit and/or the optical transceiver.
Yet another concern with conventional optical transceivers relates to the polarity of the data signal that is received by the post-amplifier, and the polarity of the data signal that is transmitted by the laser driver. Note that with respect to data signals at least, “polarity” does not refer to a positive or negative charge, but rather refers to a data value relative to, for example, a desired value. For example, if a logical “1” is transmitted where a logical “0” should have been transmitted, such data may be referred to as inversely or improperly polarized.
With particular reference now to certain exemplary data transmission methods and systems, many data transmission lines include two data paths. Because the signaling on such transmission lines is differential, a decision must be made as to how to interpret a logical “1” or “0,” in view of the fact that two data paths are involved. This implementation contrasts with use of a single data transmission line wherein an electrical or optical pulse corresponds, for example, to a “1” and no pulse corresponds to a “0.” Typically, interpretation of a logical “1” or “0” in the context of differential data paths is implemented by defining a particular relationship between the two data paths as signifying either a “1” or a “0” and then interpreting the received signal accordingly.
By way of example, it could be decided that if the first data path has a positive electrical polarity relative to the second data path, then a logical “0” is represented. As another example, it could be decided that if a predetermined voltage differential exists between the first and second data paths, a logical “1” is represented. In any event, once a particular convention is selected, it is important that the relationship between the data paths be maintained so that the appropriate significance can be assigned to the detected differential between the two paths. However, problems sometimes occur that may compromise this relationship, and thus the error rate, among other things, of the transmitted data.
For example, as the data, in the form of a predetermined relationship such as those described above, is received, processed and/or transmitted by various system components, the data may become inverted so that a transmitted “1” becomes a “0” at some point in the system. As suggested above, such inversion may take the form, for example, of a reversed electrical polarity between the data paths. Data inversion may result, for example, from operations performed by of one or more of the system components, and/or from effects imposed by various conditions occurring within the operating environment of the system. In any case, such data inversion is problematic. For example, the inversion of all the “1”s in a data stream to “0”s would result in a one hundred percent error rate, an undesirable result.
In yet other cases, data inversion may result from the physical arrangement of the system circuitry. By way of example, if the data paths are somehow reversed during construction of the PCB, and such reversal is not identified and compensated for in some manner, data inversion will likely result.
In view of the foregoing, it would be useful to be able to integrate the driver and post-amplifier in such a way that their respective functionalities could be implemented in a single-sided PCB, while at the same time minimizing redundant components and functionality. Moreover, the integrated driver and post-amplifier should include, or be configured to interface with, a single digital control interface that will serve to enhance the flexibility and functionality of the optical transceiver, and related devices, by providing the ability to receive and process multiple digital control signals. Additionally, the integrated driver and post-amplifier should implement suitable digital-to-analog converters (“DAC”) which will allow conversion of digital control signals to an analog form that that can be used in the processing of various data signals, as well as in the control of certain operational aspects of components such as the optical transmitter and receiver. Finally, the integrated driver and post-amplifier should implement data signal polarity control functionality so as to reduce and/or eliminate data error rates of the system wherein the integrated driver and post-amplifier is employed.